1. Field of the Invention
The invention relates to a blood pressure measuring appliance, and particularly, to an appliance having a pulse beat detector responding to arterial pulse beats, an electrocardiograph signal detector and a blood pressure measuring and indicating apparatus.
2. Description of Related Art
Blood pressure is ordinarily measured by means of an inflatable bag connected to a mercury manometer, according to the method of Riva-Rocci. The inflated bag ties off the upper arm so that the arm artery permits no more blood to flow therethrough. On reduction of the bag pressure the blood is again forced through the slowly opening artery. Then, as a result of turbulent flow, a noise occurs to which it is possible to listen with a stethoscope. The pressure read off on the manometer corresponds, on commencement of the turbulent flow, to the systolic blood pressure. When, upon further pressure reduction in the bag, the artery opens completely, the turbulent flow changes into a laminar flow and the heard sound or noise disappears. The pressure then read off on the manometer corresponds to the diastolic blood pressure. In this measuring method the accuracy of measurement depends upon the existing physiological conditions of the patient and the hearing capacity of the physician.
It is known from "Medical & Biological Engineering & Computing", September 1981, pages 671, 672, that the pulse beat transit time varies with the blood pressure. This is utilized, in combination with a conventional blood pressure measurement bag, for the determination of the measurement moments for the systolic pressure and the diastolic pressure. The time is ascertained between the R-peak of an ECG signal detected by means of an ECG signal detector and the arrival of the pertinent pulse beat at the location of a pulse beat detector. The systolic pressure is read off at the moment of maximum time delay on the manometer of the bag. The measurement moment for the diastolic pressure is ascertained in dependence upon the speed of variation of the transit times of successive pulse beats. The fact is utilized that the transit time of successive pulse beats remains constant after the diastolic pressure is reached. In the known blood pressure measuring appliance the actual blood pressure measurement takes place according to the bag method of Riva-Rocci.
The invention is directed towards provision of a blood pressure measuring appliance which, after initial calibration, can measure the blood pressure without an inflatable bag.